Don't mix up hard work and valuable work. If a recruiter approaches you with a client for you and all you have to do is accept the job, that saves you a lot of the hassle of going out and finding a new client. If I sell you a $100 bill for $50, why should you care how much effort it took for me to get that $100 bill?
Another thought: once you get above a certain rate it ceases to make sense to work with staffing agencies. Staffing agencies in my experience usually seem to be willing to pay $30-80/hr, and I'm guessing they probably bill out at about twice what they're paying you. So if they advertise $50/hr as the rate for a particular gig, they're probably billing the client $100/hr, and if your rate is $150, that's a total no-go from the start.
My advice would be to not worry about what anyone else charges. There will always be people who charge more than you and less than you, and it varies wildly. There will always be businesses that will be absolutely shocked by a rate another business would find totally reasonable.
The way I handle my hourly rate is to get a client at $X/hr, and once I've been working at $X/hr for a few months, set a goal to get a new client at $1.5X/hr or $2X/hr by a certain date. Then $2X becomes the new $X and I repeat the process. In this way I've tripled my rate from what it originally was.
I don't share my rate publicly because I don't want a client in 2015 to say, "Well, I saw that you were charging $0.5X in 2014, so why are you asking for $X now?"